
528
Thorn,
Naish,
and
Ramamohanarao
reduce the number of buffers required for the "r" predicate, since the number
of slow bits of "r" has been fixed at zero.
The final bit to be chosen will be either Xj or Z
{
since both the sfb-vectors
<
Ύ
1
Υ
2
Χ
1
" and
ii
Y
l
Y
2
Z
l
99
would reduce the number of buffers required to
2
1
+ 2
2
+ 2° = 7 pages and 2° + 2
2
+ 2
1
= 7 pages respectively. Any more X,
Y, or Ζ bits will not further reduce the number of buffer pages required.
Some larger examples are given in Appendix 2. The algorithm guarantees
that at least one predicate will only need one buffer and produces an optimal
sfb-vector for all two-way joins. However